Patent GB-1292355-A (GB)
Title: Digital data storage circuits using transistors
IPC: H03K3/288
Filed: 1970-01-22
Abstract: 1292355 Bi-stable circuits INTERNATIONAL BUSINESS MACHINES CORP 22 Jan 1970 [27 Feb 1969] 3246/70 Heading H3T [Also in Division G4] A memory comprises a plurality of transist or cells, only one of which may be activated at a time, there being non-linear impedance means (e.g. diodes) which cause the power consump tion of the unactivated cells to be less than half of that of the activated cell. For an unactivated call to remain conducting, its conducting transistor must have the ratio of where To keep this ratio > 1 and also to keep the power consumption low, the collector lead impedance comprises two diodes. The memory device comprises a plurality of bi-stable cells 10, 33 arranged in columns and rows, a first plurality of power sources 30, 46, a second plurality of power sources 18, 35, each cell (e.g. 10) being connectible selectively to one (18) of said second plurality and one (30) of said first plurality, whereby only one cell at a time can be activated due to one of the first plurality and one of the second plurality being activated simultaneously. Normally each cell is connected to a low current source 17, 34 but, if a cell is to be activated, it is connected to a high current source (second course) 18, 35 and simultaneously a driver 30 is activated. Only one cell in a column can be connected to a high current source at a time. The driver may be an NPN transistor and it is connected to all cells in a column, each column having its own driver. Reading.-Switches 38 and 40 are connected to ground. Current flows through the conducting transistor 11 or 12 of the cell from the high current source and causes a voltage drop to occur across resistor 23. Hence line 22 rises from ground potential and a current flows through line 27 or 29, depending on whether transistor 11 or 12 is conducting, to activate a sensing device (not shown). Writing.-The cell 10 is connected to high current source 18 and driver 30 activated and one of switches 38, 42 is moved away from its ground contact, the switches being connected to lines 27, 29. The switch moved depends on whether a 0 or a 1 is to be written in. To write in via line 27, switch 40 engages contact 42 and a diode 44 keeps the potential on line 29 up when the driver 30 is energized, and only the potential on line 27 falls. If transistor 12 is conducting, current flows therethrough to emitter 24 whereby the voltage drop across resistor 23 increases. This tends to make emitter 24 positive with respect to emitter 26 but not emitter 28 which is held positive. This causes transistor 11 to turn on and transistor 12 to turn off. Power consumption.-The diodes 13, 14 and 19, 20 act as non-linear impedances for the transistors 11, 12 respectively. When a cell, e.g. 10, is being neither read from nor written into, i.e. it is connected to its low current source the voltage across cell 10 is about 1.3v. When the cell is to be read, the voltage across the cells rises to 2.6v. and the current increases exponentially due to the reduced resistance of the diodes. For all the cells in the same row as cell 10 their lines 47, 48 will be connected to positive contacts and the voltage will be about 2.2v. at a substantially smaller current. Thus the power applied to each cell in the same row will be less than half the power applied to the cell 10. The other cells in the same column as cell 10 are still at point 190 so that their power consumption is very low. A similar situation exists for write in. Other embodiments are described (Figs. 2-6, not shown) and the cells may be formed as a monolithic integrated circuit, e.g. of silicon. Only one diode may be used as a non-linear impedance or some other non-linear impedance may be used, e.g. an insulated field effect transistor of the source follower type.